A vacuum heat insulator is manufactured, for example, by coating a porous core member with an enveloping member of plastic laminate film having a gas barrier layer and a heat seal layer, and evacuating and sealing. As the sealing technology, generally, the heat sealing method for heating and pressing the junction of two plastic laminate films is employed from the viewpoint of reliability and productivity in sealing. In the vacuum heat insulator used in this manner, the enveloping member of plastic laminate film is preliminarily formed in a bag slightly larger than the core member, and the core member is inserted into the bag-shaped enveloping member, and after evacuating, the opening is sealed by heat sealing.
Accordingly, at four sides of the outer periphery of such vacuum heat insulator, peripheral parts composed only of adhered enveloping member are formed without any interposing portion of the heat seal part of the enveloping member and the core member. To use the vacuum heat insulator, therefore, various ideas are proposed for reducing the peripheral parts as much as possible.
FIG. 40 is a perspective view showing a conventional manufacturing process of vacuum heat insulator, and FIG. 41 is a perspective view showing a conventional vacuum heat insulator. In FIG. 40 and FIG. 41, a vacuum heat insulator 300 is fabricated by putting a core member 302 on a film sheet 301, folding the sheet 301 so as to wrap the core member 301, evacuating the inside of the sheet 301 in this state, folding, and fusing the mutually bonded ends of the sheet 301 by heat on three peripheral sides. At this time, when the folded position of the sheet 301 is fitted tightly to the end of the core member 302, protrusion 304 by heat sealing is not formed at the end 303 of the vacuum heat insulator 300 (this advantage is disclosed, for example, in Japanese Laid-open Patent No. H7-269781).
A conventional vacuum heat insulator is explained. FIG. 42 is a plan view of a conventional vacuum heat insulator in FIG. 43 is a sectional view of the vacuum heat insulator shown in FIG. 42 disposed in an outer box of a heat insulated box.
In FIG. 42, a vacuum heat insulator 314 is composed by coating three rectangular core members 311 with a gas barrier film 312. The inside of the film 312 is kept in an evacuated state of, for example, about 10 Pa or less. The three core members 311 are disposed nearly on a same plane at a mutual specified spacing in one direction, and a film is heated and fused between one core member 311 and other core member 311 so that the three core members 311 may be positioned in an individual independent space. In the heat seal portion 313 between adjacent core members 311, a folding line 314a for folding is provided (for example, Japanese Laid-open Patent No. H7-98090).
The vacuum heat insulator 314 is provided, for example, in the inside of an outer box 315 of a heat insulated box such as refrigerator as shown in FIG. 43. The outer box 315 is a U-shaped metal plate 316. The vacuum heat insulator 314 is adhered and fixed to the metal plate 316 before U-shape bending so that the folding line 314a of the vacuum heat insulator 314 may coincide with the folding line of the metal plate 316. By U-shape bending of the metal plate 316 to which the vacuum heat insulator 314 is adhered and fixed at the side facing the inside of the outer box 315, the outer box 315 having the vacuum heat insulator 314 in its inside is obtained as shown in FIG. 43.
However, as disclosed in Japanese Laid-open Patent No. H7-269781, although heat seal part is not formed at one end of the vacuum heat insulator, heat seal parts 313 are present in the remaining three peripheral sides. Yet, since the enveloping member of a bag shape is formed somewhat larger preliminarily in order to put in the core member 311, when the inside is evacuated, the portion composed only of the enveloping member without provided with the core member 311 is left over between the core member 311 and heat seal part 313. Accordingly, the width of the peripheral edge formed around the core member is increased, and when the vacuum heat insulator is applied, folding process of the peripheral edge is needed.
Besides, since the portion composed only of the enveloping member not provided with core member is formed between the core member 311 and heat seal part 313, the shape of the vacuum heat insulator is limited, and it was difficult to manufacture a vacuum heat insulator in a desired shape.
In the vacuum heat insulator disclosed in Japanese Laid-open Patent No H7-98090, plural rectangular core members are disposed nearly on a same plane at a mutual specified spacing in one direction. Each folding line formed in the core member and the heat seal portion positioned between one core member and adjacent core member is almost parallel to each other. Therefore, applicable objects of the conventional vacuum heat insulator (by adhering or gluing) are limited to sides of objects not changed in the shape and size of the plane and cross section in the longitudinal direction, such as sides of an object of polygonal and polyhedral columnar shape having three or more corners in cross section, or inner side or outer side of a polygonal tubular object having three or more corners in cross section. It was hence difficult to apply the conventional vacuum heat insulator, for example, in place of down or cotton of body warmer (Outfit for protection against cold).